Tips for growing tomatoes: Watering and fertilizing


Look at all those grape tomatoes! They’ll be ready for harvest just when we go on vacation next week. There’s nothing I can do about that, but I can do a lot of things that will help me get a large and delicious harvest.

Recently I wrote about tieing and staking tomato plants. Doing those chores consistently and correctly will certainly improve the health of your plants and as a result your overall harvest. So will correct watering and fertilizing, the topic of this post.


Tomato plants are big, and so are their root systems. Assume that the height of the plant is the same as the depth of the roots–a 5′ high plant has roots that are at least 5′ deep. So that plant needs deep watering, not a little sprinkle every day or so. Shallow watering causes shallow roots and weak plants.

When tomato plants are actively growing in late spring and early summer, they need heavy watering–1-2″ per week. The higher figure applies to the beginning of the season, when the plants are growing fast. Once you begin to harvest fruit, cut back a bit on the watering to avoid cracked fruit. But continue to water deeply and consistently to avoid problems like blossom end rot (the bottoms of the fruits turn black because of not enough water).

How do you know how much water you’re giving your plants? I use a highly technical and sophisticated rain gauge. It consists of a large, open flat-bottomed container (a 1-quart yogurt container works well) placed on the ground among the plants. When I water, I check the depth of water in the container  from time to time, and when I see the right amount of water in the container, I stop. (Leave the container there all the time–it will also tell you when you’ve had enough rain to omit supplemental watering.)

Another important point is to water early in the morning so the plants have plenty of time to dry off before nightfall. This helps prevent the spread of fungal diseases. Anytime before noon is fine. If you can devise a watering system that doesn’t wet the foliage, that’s much better, of course, but watering early will work nearly as well.

How often to water? Remember that 1-2″ per week rule. So if there’s been no rain at all, once a week. Check the rain gauge.


It’s all about the soil. If your soil is loose and full of organic matter, you may not need to fertilize at all. I rely on homemade compost–two or three loads per season–to enrich my soil consistently and evenly, and I never fertilize my vegetable plot. If you really feel you must fertilize, because the leaves look pale or just because you think you must, avoid high-nitrogen fertilizers. Nitrogen causes plants to make leaves, not fruits. And stick with organic products to preserve your soil structure.

So it’s really pretty simple–water deeply and seldom, know how much water your plants are receiving, and fertilize only if necessary and then with organic, low-nitrogen fertilizer.

I picked my first few tomatoes today–lovely yellow grapes. Notice the cracks, because we got a lot of rain while they were forming. There’s nothing anyone can do about that.



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